Recently, many sectors of society have increasingly viewed the sun as a viable and desirable alternative source of energy. Solar energy is non-polluting, abundant and immune to geopolitical factors. Moreover, it is virtually inexhaustable (contrast the Earth's finite supply of fossil fuels) and free from the potential dangers often associated with nuclear power.
Indeed it has been estimated that solar energy impacts the surface of the United States at a rate of approximately 5.56.times.10.sup.19 BTU's/year (5.87.times.10.sup.22 joules/year). Considering that the U.S. consumed 7.8.times.10.sup.16 BTU's (8.23.times.10.sup.19 joules) in 1978, it goes without saying that by tapping even a modest portion of the sun's energy, we can appreciably reduce out dependence on dwindling fuel reserves.
In order to take advantage of this relatively free largesse, various solar energy systems have been proposed and developed. This particular disclosure pertains to a method for improving the production of electrodes for photovoltaic cells.
Photovoltaic cells produce an electrical current by the excitation of electrons by photons. Briefly, certain semiconductors (CdSe, for example) can be directly stimulated by light to generate an electrical current. Although the physics of this process are now well understood, it suffices to say that when a photon of a specific minimum energy level collides with a valence electron, the photon, by imparting its energy to the electron, "kicks" the electron into a higher energy or conduction band while simultaneously leaving a hole (vacancy) in the lower energy valence band. These charge carriers (both the electron and the hole) can be made to move (and thus generate electric current) by having them generated near or within a field region created at some form of semiconductor interface, e.g., metal--semiconductor, n-semiconductor--p-semiconductor, or semiconductor--electrolyte interface. The type of cell utilizing the junction produced at the last interface is known as a photoelectrochemical cell and is the type used to test the electrodeposit made in this disclosure. However, it should be appreciated that the semiconductor electrodeposits produced by the disclosed procedure need not necessarily be restricted to this type of photocell.
More specifically, our invention relates to the production of thin film semiconductor photoelectrodes. Although presently employed in light meters, security devices, etc., it is quite conceivable that this technology will find a place in the wholesale production of electric power.
Presently, cadmium-selenium semiconductors utilized in thin film semiconductors are electrodeposited onto substrates having relatively high electrical conductivities. Typically, these Cd-Se electrodes are prepared in an acid sulfate bath of very low pH (typically 0-1 pH units). This electrolytic solution may prove to be of limited usefulness in that it is believed that an acid sulfate bath may restrict the amount of Se-Cd deposition to a narrow stoichiometric range. This range limiting characteristic of acid sulfate baths may be undesirable in instances where it is necessary to deposit cadmium and selenium over a broad, nonstoichiometric range.
Clearly, a method to facilitate the codeposition of Cd-Se is desirable.